The present invention generally relates to peer-to-peer communication and, more particularly, to an apparatus for peer-to-peer communication over a Universal Serial Bus (USB) link.
As the demand for high speed communication between hosts (for example, personal computers) and peripheral devices (for example, media players or optical storages) grows, Universal Serial Bus (USB) specification has been developed and taken into practice for decades to fulfill such demand. The USB 2.0 specification specifies and provides for direct communication between a host and a peripheral device (or a plurality of peripheral devices) through a USB link at a speed up to 480 megabits per second (Mbps). In addition, the USB “on the go” (OTG) specification that supplements the legacy USB 2.0 specification further allows direct device-to-device communication through a USB link, without using any host as an intermediate bridge between the devices.
For achieving higher transmission bandwidth of host-to-device or device-to-device communication over the USB link, USB 3.0 specification has been released, in which the transmission rate is further enhanced to 5 gigabits per second (Gbps), approximately ten times of the transmission rate of the USB 2.0 specification. The USB 3.0 specification may further provide for direct host-to-host communication via a USB link without any intermediate bridge therebetween, as will be discussed below.
FIG. 1 is a block diagram of a peer-to-peer communication system 100 using a USB link 1-lk in prior art. Referring to FIG. 1, the system 100 may include a first peer unit 11-1 and a second peer unit 11-2. The first and second peer units 11-1 and 11-2 may include a first host and a second host, respectively, each of which has a USB 3.0 compliant host controller interface (HCI) or extensible HCI (i.e., xHCI) and a USB 2.0 compliant HCI (i.e., EHCI). A peer-to-peer communication (i.e., host-to-host communication in this example) between the first host 11-1 and the second host 11-2 may be established over the USB link 1-lk through a USB 3.0 compliant receptacle 12-1 of the first host 11-1, a USB 3.0 cable 14 with USB 3.0 plugs 13-1 and 13-2 and a USB 3.0 compliant receptacle 12-2 of the second host 11-2. Specifically, the first and second hosts 11-1 and 11-2 may negotiate with each other, determine which one to operate as a host while the other one to operate as a device, and perform a “physical” host-to-device communication that may in turn achieve a “virtual” host-to-host communication. As a result, the first and second hosts 11-1 and 11-2 may communicate with each other directly without any intermediate bridge. However, such host-to-host communication is available only in the presence of a USB 3.0 cable 14 with a pair of USB 3.0 plugs 13-1 and 13-2 in conjunction with a pair of USB 3.0 receptacles 12-1 and 12-2. Accordingly, the peer-to-peer communication system 100 may only allow direct host-to-host communication over a USB link through a USB 3.0 cable with the both hosts compliant with the USB 3.0 specification.
It may therefore be desirable to have an apparatus that allows direct peer-to-peer communication over a USB link between a pair of USB 2.0 hosts, a pair of USB 2.0 devices, and between a USB 3.0 host and a USB 2.0 host, in addition to a pair of USB 3.0 hosts.